1. Field of the Invention
The present invention relates to a digital watermark embedding apparatus and method to embed a digital watermark in contents, and a digital watermark detection apparatus and method to detect a digital watermark from contents.
2. Description of the Related Art
In recent years, fields handling digital contents increase due to development of a computer and a network. The digital contents have features capable of making exactly the same contents as original contents with a very low cost. For this reason, an anti-illegal copy measure of a digital copyrighted work becomes indispensable.
Digital Watermarks wherein additional information is embedded in digital contents in the degree that a person cannot find the additional information are broadly discussed and developed as one of an anti-illegal copy measure for allowing insistence of a copyright broadly.
There is a digital watermark technology for embedding digital watermark in a difference between frames (refer to JP-A 2003-174631(KOKAI), for example). In this technology, a digital watermark is embedded in contents by overlapping a pattern of the first watermark on the frame of the frame number f, and a pattern of the second watermark generated by inverting the polarity of the pattern of the first watermark in the frame of the f+1 frame number. The digital watermark is detected by obtaining a difference between the frame of the f frame number and the frame of the f+1 frame number.
However, in the case that the difference between the frames before embedding the digital watermark is large (for example, in the case of the scene with large movement in video contents), there is a problem that a very large noise component is detected along with the watermark component, resulting in causing false detection.
In the conventional method for embedding a digital watermark by overlapping watermark patterns reversed in polarity to each other on two frames, respectively, and detecting the digital watermark by obtaining a difference between the frames, when the difference between the frames is large, it sometimes fails to detect a watermark pattern exactly.